In the manufacture of titanium dioxide by the so-called chloride process, raw materials containing titanium are chlorinated at high temperatures in the presence of a compound containing carbon. The metal oxides contained therein are almost completely converted into the corresponding metal chlorides in the process. The gas leaving the chlorinator is cooled in a multi-stage process, and unreacted, dust-like educts, metal chlorides of relatively low volatility and titanium tetrachloride are separated. The gas remaining after the final stage still contains traces of highly volatile metal chlorides, typically 0.1 to 0.5% by volume TiCl4, 0.1 to 0.5% by volume SiCl4 and 0.5 to 9% by volume dry HCl.
The statutory regulations concerning the prevention of water and air pollution prescribe the cleaning of exhaust gases containing TiCl4 and/or SiCl4 prior to their being discharged into the environment. In addition, there are economic grounds for putting the residual materials occurring during a cleaning process of this kind to the most extensive possible industrial use.
DE 33 28 675 C2 ( U.S. Pat. No. 4,533,530) describes a method for cleaning exhaust gases containing TiCl4 from the chlorination of raw materials containing titanium, in which the exhaust gases come into contact with aqueous titanium oxychloride solution in a spray column.
Connected directly downstream of the spray column, without intermediate separation, is an additional scrubbing device, e.g. an ring-slot scrubber, for increasing the absorption efficiency to roughly 99%. The titanium oxychloride solution with a concentration corresponding to 100 to 170 g TiO2/l is circulated via the spray column and the ring-slot scrubber in a common circuit, the concentration being controlled by adding water or hydrochloric-acid solutions to the spray column. Exhaust gases, now largely free of gaseous TiCl4, pass to a separate stage to produce industrially useable HCl.